1. Technical Field
The present invention relates to dynamic comparators, and, more particularly, to a dynamic comparator with equalization function.
2. Description of Related Art
Comparators that compare the difference between input signals and output the result of the comparison have been widely used in electronic equipment or electronic devices.
For example, a general dynamic comparator is dynamically switched between reset and comparing mode. The dynamic comparator comprises a preamplifier and a switched latch. The preamplifier is used to amplify input signals and applies its output signals to the switched latch, so that the sensitivity of the comparator can be improved. The switched latch receives the output signals of the preamplifier and performs signal regeneration. The performance of a comparator can be evaluated based on power consumption and operating speed, and a method of quantifying performance is based on the energy consumption of the comparator (in units of Joules), that is, the power consumption divided by operating speed.
Kobayashi et al. disclosed a comparator structure in IEEE JSSC'93. The comparator structure has the characteristics of a high-impedance input, but its high transistor stack limits the supply voltage, and the size of the tail current is determined by only one transistor, resulting in the design trade-off between speed and accuracy. Moreover, the speed and accuracy of this architecture is more sensitive to input common-mode variation.
A double-tail comparator structure proposed by Schinkel et al. in IEEE ISSCC'07 reduces the stack number of the transistors from four transistors to three transistors, allowing the supply voltage to be further reduced. Also, based on the double-tail structure, the operating speed and accuracy of the comparator can be optimized respectively. For example, the tail current of the first stage in the comparator can be used for accuracy optimization, and the other tail current for the second-stage can be used for speed optimization. Therefore, the speed and the accuracy of the comparator can be insensitive to input common-mode variation.
In order to further enhance the operation speed of the comparator, a comparator structure disclosed in U.S. Pat. No. 8,111,090 can be adopted, that is, equalization function is added. As such, the operating speed of the comparator can be enhanced. It is worth mentioning that such equalization function needs to be provided in the structure of a static circuit. In other words, the comparator includes DC power consumption.
In this regard, there is a need for a comparator with low power consumption and high speed operation based on equalization techniques have no DC power consumption and, in particular, does not compromise the accuracy of the comparator.